Since decibels are always comparisons ______ are required to use decibels.

Since decibels are always comparisons ______ are required to use decibels.

• A. One intensities
• B. Two intensities
• C. Three intensities
• D. None

Answer: (B)

Decibels are a logarithmic measure of a ratio, not an absolute quantity. They express how large one quantity is compared to another by taking the log of the ratio. Because of that, you always need a pair to form that ratio: the level you’re measuring and a reference level. In acoustics, this appears as either an intensity ratio (dB = 10 log10(I1/I0)) or a pressure ratio (dB = 20 log10(p1/p0)), where I0 or p0 is the reference value. Without a reference, there’s no ratio to log, so a single intensity value can’t be expressed in decibels. That’s why the correct answer is two intensities: you compare the measured intensity to a reference intensity (or, equivalently, compare two levels).

Decibels are a logarithmic measure of a ratio, not an absolute quantity. They express how large one quantity is compared to another by taking the log of the ratio. Because of that, you always need a pair to form that ratio: the level you’re measuring and a reference level. In acoustics, this appears as either an intensity ratio (dB = 10 log10(I1/I0)) or a pressure ratio (dB = 20 log10(p1/p0)), where I0 or p0 is the reference value. Without a reference, there’s no ratio to log, so a single intensity value can’t be expressed in decibels. That’s why the correct answer is two intensities: you compare the measured intensity to a reference intensity (or, equivalently, compare two levels).